A liquid crystal display apparatus has an illuminating device provided on a front or back surface of a liquid crystal panel. A light source provided on a back surface of a liquid crystal panel is generally called a “backlight”, which is categorized as either a direct type backlight, which has a light source disposed directly under a liquid crystal panel, or an edge light type backlight, which has a light source disposed on a lateral side of a light-guiding member and thereby achieves a surface light source.
Both of the types of backlight generally use cold-cathode fluorescent tubes as their light sources. However, in recent years, an illuminating device using mercury-free light-emitting diodes as a light source has been developed out of environmental concerns.
Cases where white illuminating devices are obtained by using light-emitting diode as light sources are categorized into (i) a case where a white illuminating device is obtained by using white light-emitting diodes each of which is a combination of a blue light-emitting diode and a yellow light-emitting fluorescent material and (ii) a case where a white illuminating device is obtained by disposing plural sets of monochromatic light-emitting diodes of different colors such as red, green, and blue and by mixing their colors. Recently, a backlight, capable of expressing a wide range of color reproduction, in which red, green, and blue monochromatic light-emitting diodes are used in combination has been attracting attention.
For example, liquid crystal televisions (LE-40M91B) each including a direct type backlight in which red, green, and blue monochromatic light-emitting diodes are used in combination have been mass-produced. In a set of light-emitting diodes of the three primary colors in which red, green, and blue light-emitting diodes are used in combination, it is necessary to mix the colors of the light-emitting diodes so as to produce white light. For this purpose, the light-emitting diodes are placed at a certain distance from a diffusing plate required for obtaining uniform light, whereby a uniformly-white backlight is achieved.
In a uniformly-white edge light type backlight obtained by combining red, green, and blue monochromatic light-emitting diodes, light-emitting diodes of the same color are disposed at intervals of not less than 10 mm in consideration of the intervals at which they are mounted, because each of the light-emitting diodes has a width of approximately 3 mm. This requires a special way of mixing colors of emitted light. Lumileds Lighting, LLC proposes a method in which a color-mixing section for mixing colors of emitted light is not used as a display section (Non Patent Literature 1). As described in this method, in order to obtain a uniformly-white backlight by combining red, green, and blue monochromatic light-emitting diodes, it is necessary to provide (a) a color-mixing section for mixing colors of emitted light and (b) a display section that glows white.